Calculate your Body Mass Index instantly using metric or imperial measurements.
Body Mass Index (BMI) is a measurement calculated from your height and weight that is used to screen for weight categories that may lead to health problems. It was developed in the 1830s and remains the most widely used initial screening tool worldwide.
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lbs) ÷ height (inches)²
BMI is a useful population-level screening tool but has limitations at the individual level. It doesn't differentiate between muscle and fat mass — a bodybuilder may have a high BMI despite low body fat. It also doesn't account for age, ethnicity, or fat distribution. Always consult a healthcare professional for a full health assessment.
BMI uses a simple formula: weight in kilograms divided by height in metres squared (kg/m²). In imperial units: [weight in pounds ÷ height in inches²] × 703. For example, someone who is 175cm (5'9") and weighs 75kg has a BMI of 75 ÷ (1.75²) = 75 ÷ 3.0625 = 24.5, placing them in the healthy weight range.
BMI was designed as a population-level screening tool, not a precise measure of individual health. Its main limitations: it doesn't distinguish between fat and muscle (a muscular athlete may have a "obese" BMI), it doesn't account for where fat is stored (abdominal fat is more dangerous than fat elsewhere), and it doesn't adjust for age (older adults with the same BMI as younger adults have more body fat). Waist circumference is often a better metabolic health indicator than BMI alone.
BMI and body fat percentage are related but different. Two people with identical BMIs can have very different body compositions. A person with high muscle mass might have a BMI of 27 with only 12% body fat, while another with 27 BMI might have 30% body fat. For a more accurate assessment of body composition, use our Body Fat Calculator which uses the Navy circumference method.